Heating apparatus



Oct 1956 w. D. RYCKMAN, JR 2,767,291

HEATING APPARATUS Filed April 7, 1954 FIG. I

II p I6 [SB I91 l5 IB FIG. 3 FIG. 2

7 f5 filflz 8 fill A INVENTOR.

WILLIAM D. RYCKMAN. JR.

HIS ATTORNEY United States Patent HEATING APPARATUS William D. Ryckman, Jr., Buechel, Ky., assignor to General Electric Company, a corporation of New York Application April 7, 1954, Serial No. 421,591

9 Claims. (Cl. 219-1055) This invention relates to heating apparatus, and more particularly to oven-type heating devices energized by high frequency electromagnetic energy.

One of the problems encountered in the operation of resonant cavity type heating devices is the loss of electromagnetic energy from the edge of the door opening which provides access to the cavity. Such losses reduce the efiiciency of the heating device, may cause high frequency burns if a person comes in contact with the door edge, and are likely to cause interference in the radio frequency spectrum.

Accordingly, an object of the present invention is to provide high frequency heating apparatus including an improved door structure for the access opening so arranged that the loss of high frequency energy from around the access opening is minimized or substantially eliminated.

Another object of the invention is to provide high frequency heating apparatus including an improved door structure for the access opening so arranged that interference with the wave characteristics of the apparatus is minimized.

Further objects and advantages of my invention will become apparent as the following description proceeds, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Briefly stated, in accordance with one aspect of my invention, I provide an oven-type heating device in the form of a resonant cavity or enclosure in which standing electromagnetic waves are produced in accordance with a predetermined pattern or mode by means of high frequency energy supplied by any suitable means. An access opening in the cavity is so arranged that material to be heated such as food products or the like may be inserted therein, and the opening is closed by a door structure of a configuration such that the joint between the door and the cavity is not traversed by current flowing on the inner surfaces of the cavity walls and the door. By arranging the edges of the door opening generally parallel to the paths of current flow along the walls of the cavity, substantially no currents will flow between the door structure and the cavity itself, and hence no voltage will appear across the joint to cause radiation.

For a better understanding of my invention reference is made to the accompanying drawing in which:

Fig. l is a perspective view of a resonant cavity type heating device incorporating my invention.

Fig. 2 is a developed view of the structure of Fig. 1, showing the top and sides spread out as they appear before the structure is assembled.

Fig. 3 is a top plan view of the structure shown in Fig. 1, some of the parts being broken away to show details of construction.

Referring now to Figs. 1 to 3 of the drawing, the reference numeral 1 designates a resonant cavity type heating enclosure designed for operation in the TEIOI mode and 2,767,291 Patented Oct. 16, 1956 formed by metallic top wall 2, bottom wall 3, side walls 4 and 5, and rear wall 6. Side walls 4 and 5 and rear wall 6 are rectangular in shape, but the front edge of top wall 2, and also bottom wall 3, is indented in the form of a V-shaped notch having its vertex located midway between opposite corners of Walls 2 and 3 respectively. Thus the front edge of top wall 2 includes intersecting straight edge portions 7 and 8, while the front edge of bottom wall 3 includes intersecting straight edge portions 9 and 10. Edge portions 7 and 9 lie in a plane intersecting the front edge of side wall 4 and the rear edge of side wall 5, while edge portions 8 and 10 lie in a plane which intersects the front edge of wall 5 and the rear edge of wall 4.

In the illustrated embodiment the side and rear edges of top wall 2 and bottom wall 3 have the same dimension and thus edge portions 7 and 8 of top wall 2 and edge portions 9 and 10 of bottom Wall 3 form V-shaped notches having an included angie of degrees. However, it should be apparent that rectangular enclosures having other dimension ratios may be utilized (in which case the included angle of the notch may be greater or less than 90 degrees), and that in some cases a curved or parabola shaped indentation in the front edge of the cavity may be used rather than a front edge in the form of a V-shaped notch.

The access opening formed by edge portions 7 and 8 of top wall 2 and edge portions 9 and 10 of bottom wall 3 may be closed by a closure or door structure 11 preferably hinged to the front edge of side wall 5 by means of a hinge 12, for example. Door 11, which may be formed from sheet metal, includes a rectangular front panel 13, and top and bottom triangular panels 14 and 15. Panels 14 and 15 are so shaped that when door 11 is closed, they fit snugly Within the notches in the front edges of top and bottom walls 2 and 3 respectively. Thus when the door is closed, edges 16 and 17 of panel 14 are parallel to edges 7 and 8 of top wall 2, and edges 18 and 19 of panel 15 are parallel with edges 9 and 10 respectively of bottom wall 3. To provide a convenient means for opening and closing door 11, a handle 20 secured to the outer surface of panel 13 may be provided. It is not necessary that the door 11 make continuous contact with the adjoining edges of the access opening. This is an important feature inasmuch as it eliminates the need for maintain ing a clean close fitting joint.

Cavity or enclosure 1 is designed to operate in the TEior mode and accordingly is preferably supplied with electromagnetic energy by a coupling loop 21 extending through an opening 22 in the central portion of rear wall 6, the loop 21 being fed through a coaxial line 23 connected to a suitable source of high frequency electric energy (not shown). Loop 2% lies in a plane substantially parallel to the side walls 4 and 5 and thus provides suitable coupling between the cavity and coaxial line 23.

In operation, food to be cooked or material to be heated is placed in the cavity in substantially the center of bottom wall 3, it being observed that a portion of the container for the food or material may overhang the access opening (i. e. the space adjacent the intersection of edges 9 and 10) without interfering with the closing of door 11. Energization of ca ity 1 in the TElDl mode produces a vertical electric field surrounded by a magnetic field in time quadrature therewith. Equal and opposite charges exist on the top and bottom walls 2 and 3, the charge density being a maximum at the center and zero at the side walls. Thus current flow between the central portions of the top and bottom walls takes place as illustrated by the arrows in Fig. 2, it being noted that the current flow is substantially parallel to the vertical edges of the enclosure as well as edges 7, 8, 9 and 10 on the cavity itself and edges 16, 17, 18 and 19 on the door structure 11.

itself and no electric potential exists across the opening between the edges of the door and the edges of the cavity. While the electric and magnetic fields inside the cavity may be somewhat distorted by food or other material placed therein, the resulting current flow across the door joint is relatively small, and the radiation resulting from such distortion is generally insignificant as compared with radiation losses from cavities having a conventional door arrangement.

While I have shown a particular embodim nt of my invention, I do not desire my invention to be limited to the particular construction shown, and I intend in the appended claims to cover all modifications within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A high frequency heating enclosure comprising rectangular side and rear walls, and top and bottom walls with side and rear edges of equal length co-extensive with the top and bottom edges of said side and rear walls respectively, said walls having electrically conducting inner surfaces, the front edges of said top and bottom walls being in the form of a V-shaped notch having an included angle of approximately 90, and a door having an electrically conducting inner surface for closing the front opening in said cavity, the edges of said door being coextensive with the front edges of said top, bottom and side walls.

2. A high frequency heating enclosure comprising rectangular side Walls, a rectangular rear Wall perpendicular thereto, and top and bottom walls with side and rear edges co-extensive with the top and bottom edges of said side and rear walls respectively, said Walls having electrically conducting inner surfaces, the front edges of said top and bottom walls being in the form of a notch and comprising edge portions each lying substantially within a plane which is perpendicular to said top and bottom walls and which intersects the front edge of one of said side Walls and the rear edge of the other side wall, and a door having an electrically conducting inner surface for closing the front opening in said cavity, the edges of said door being coextensive with the front edges of said top, bottom and side walls.

3. High frequency heating apparatus comprising a cavity having rectangular side walls, a rectangular rear wall perpendicular thereto, and top and bottom walls with side and rear edges co-extensive with the top and bottom edges of said side and rear walls respectively, said walls having electrically conducting inner surfaces, the front edge of said top wall being in the form of a notch and compris ing edge portions each lying substantially within a plane which is perpendicular to said top and bottom walls and which intersects the front edge of one of said side walls and the rear edge of the other side wall, a door for closing the front opening in said cavity, said door including a rectangular front panel and a triangular top panel, said panels having electrically conducting inner surfaces, the edges of said door being co-extensive with the front edges of said top, bottom and side walls, and means for supplying high frequency electromagnetic waves to the interior of said cavity.

4. High frequency heating apparatus comprising a cavity having rectangular side and rear walls, and top and bottom walls with side and rear edges of equal length coextensive with the top and bottom edges of said side and rear walls respectively, said walls having electrically conducting inner surfaces, the front edges of said top and bottom walls being in the form of a ti-shaped notch having an included angle of approximately 90, a door having an electrically conducting inner surface for closing the frontv opening in said cavity, the edges of said door'being co-extensive with the front edges of said top, bottom and side walls, and means for supplying to the interior of said 4 t cavity high frequency electromagnetic waves having a wavelength such that the cavity is energized in the TE101 mode.

5. High frequency heaving apparatus comprising a cavity having rectangular side Walls, a rectangular rear wall perpendicular thereto, and top and bottom walls with side and rear edges co-extensive with the top and bottom edges of said side and rear walls respectively, said walls having electrically conducting inner surfaces, the front edges of said top and bottom walls being in the form of a V-shaped notch and comprising edge portions each lying within a plane which is perpendicular to said top and bottom walls and which intersects the front edge of one of said side walls and the rear edge of the other side wall, a door having an electrically conducting inner surface for closing the front opening in said cavity, the edges of said door being co-extensive with the front edges of said top, bottom and side walls, and means for supplying to the interior of said cavity high frequency electromagnetic waves having a wavelength such that the cavity is energized in the TE101 mode.

6. High frequency heating apparatus comprising a me tallic cavity having rectangular side walls, a rectangular rear wall perpendicular thereto, and top and bottom Walls with side and rear edges co-ext-ensive with the top and bottom edges of said side and rear walls respectively, the front edges of said top and bottom walls being in the form of a V-shaped notch and comprising edge portions each lying within a plane which is perpendicular to said top and bottom walls and which intersects the front edge of one of said side walls and the rear edge of the other side wall, a metallic door for closing the front opening in said cavity, the edges of said door being co-extensive with the front edges of said top, bottom and side walls, and means for supplying to the interior of said cavity high frequency electromagnetic waves having a wavelength such that the cavity is energized in the TE101 mode.

7. High frequency heating apparatus comprising a metallic cavity having rectangular side and rear Walls, and top and bottom walls with side and rear edges of equal length co-extensive with the top and bottom edges of said side and rear walls respectively, the front edges of said top and bottom walls being in the form of a V-shaped notch having an included angle of approximately degrees, a metallic door for closing the front opening in said caw'ty, the edges of said door being co-extensive with the front edges of said top, bottom and side walls, and means for supplying to the interior of said cavity high frequency electromagnetic waves having a wavelength such that the cavity is energized in the TE101 mode.

8. High frequency heating apparatus comprising a metallic cavity having rectangular side and rear walls, and top and bottom walls with side and rear edges of equal length co-ex-tensive with the top and bottom edges of said side and rear walls respectively, the front edges of said top and bottom walls being in the form of a \l-shaped notch having an included angle of approximately 90, a metallic door for closing the front opening in said cavity, said door including a rectangular front panel and top and bottom triangular panels, the edges of said door being coextensive with the front edges of said top, bottom and side walls, and means for supplying to the interior of said cavity high frequency electromagnetic waves having a Wavelength such that the cavity is energized in the TE101 mode.

9. High frequency heating apparatus comprising a cavity having rectangular side walls, a rectangular rear wall perpendicular thereto, and top and bottom walls with side and rear edges co-ex-tensive with the top and bottom edges of said side and rear walls respectively, said walls having electrically conducting inner surfaces, the front edges of said top and bottom walls being in the form of a V-shaped notch and comprising edge portions each lying within a plane which is perpendicular to said top and bottom walls and which intersects the front edge of one of said side walls and the rear edge of the References Cited in the file of this patent other side wall, .a .door for closing the front opening in said cavity, said door including a rectangular front panel UNITED STATES PATENTS and triangular top and bottom panels, said panels having 2,356,044 Foukes Aug. 15, 1944 electrically conducting inner surfaces, the edges of said 5 2,500,676 Hall et a1 Mar. 14, 1950 door being co-extensive with the front edges of said top, 2,527,908 Blitz Oct. 31, 1950 bottom and side Walls, and means for supplying to the 2,534,876 Ortusi et al Dec. 19, .1950 interior of said cavity high frequency electromagnetic 2,560,353 Kerwien July 10, 1951 waves having a wavelength such that the cavity is ener- 2,632,090 Revercornb et al Mar. 17, 1953 gized in the TE10 mode. 10 2,648,760 Hall et al Aug. 1 1, 1953 

